Power generation from mechanical vibration usually uses ambient vibration around the power harvesting device as a source of energy. The power harvesting device converts the ambient vibration into useful electrical energy, in order to increase energy efficiency or power other devices. Some examples of conventional methods of harvesting energy from a vibrating system include using mechanical vibration to apply strain energy to a piezoelectric material or to cause relative displacement between a magnet and coil. These methods usually involve the use of very low reliability materials. Additionally, these methods usually depend on significant relative motion, which is difficult to implement at high frequency.
Many types of vibration energy harvesters are known in the literature. At least two of the common types include (1) Harvesters that utilize magnets that move relative to conductive coils so as to generate an induced current and/or voltage within the coils, and (2) Harvesters that utilize piezoelectric elements that undergo stress changes resulting in electric current and/or voltage in these elements.
While viable for very small scale power production, both of these approaches have specific difficulties in scaling up to power levels of 0.1 W or above, and more specifically 1 W or above, especially if such power production is to be maintained across a wide-range of vibration frequencies.
Moving magnet designs depend on significant relative motion to be able to produce significant power. At the high frequency (about 10-500 Hz), which represents a moderate acceleration (1-10 Gs) vibration environment typical of many types of machinery, the high displacements needed to make watts (i.e., one watt or more) of power are difficult to achieve in moving magnet designs. Further, if more powerful magnets are used to increase power density, cogging forces/torques become difficult to overcome and structural stiffness requirements become exceedingly more demanding.
Piezoelectrics, being semiconducting ceramics, have intrinsic issues related to high internal resistance and/or high internal impedance, and low structural reliability that prevent them from being usefully scaled up for broad band power generation of the order of even watts (i.e., one watt or more) and have thus been largely limited to the micro-watt to milli-watt ranges.
Power generation using other magnetostrictive elements have been explored, such as galfenol and other magnetostrictive materials, but have encountered difficulties regarding design, power density, and prohibitive costs for achieving effective power generation.